1. Field of the Invention
The present invention relates to a variable power lens with a variable focal length, and in particular relates to a variable power lens equipped with a driving mechanism for controlling the positions of a plurality of lens groups in an optical axis direction.
2. Description of the Related Art
In conventional variable power lenses such as zoom lenses or varifocal lenses, it is often the case that a plurality of lens groups are guided in an optical axis direction by different types of cams (e.g., cam grooves or slots) formed on a single cam ring, such as in the lens barrel disclosed in Japanese Unexamined Patent Publication No. 2006-145562. In addition, a specific lens group is moved in an optical axis direction by a mechanism different from that for power variation when a focusing operation is carried out.
However, in the case where the variable power lens is provided in a lens barrel with a large intermediate member that is so large as to partition an internal space of the lens barrel, there is a possibility of a rotational ring such as a cam ring interfering with such an intermediate member, and accordingly, it is sometimes difficult for the variable power lens to be provided therein with a long rotational ring having a long length in an optical axis direction. For instance, this restriction tends to arise in a particular type of camera lens for CCTV (closed-circuit television) cameras in which a large auto iris is installed at some midpoint in an optical system.